Electric machines are generally provided with at least one coil or winding. These coils are usually formed by one or more insulated conductors having many concentric turns. Depending on the design of the machine, the coil or coils must be cooled so as to keep their operating temperature within a desired range. However, the coils are usually cooled by air, oil or other coolant circulating over the exterior turns thereof. The turns of the coils that are inside may not contact the coolant as well, and may only be cooled through heat conduction with the turns closer to the effective heat transfer surface(s). Also, the shape of the coil conductors is typically optimized for electrical performance, which may not necessarily result in good heat transfer properties. It would therefore be desirable to improve the cooling of coils.